Submucosal tissues of warm-blooded vertebrates are useful in tissue grafting materials. For example, submucosal tissue graft compositions derived from small intestine have been described in U.S. Pat. No. 4,902,508 (hereinafter the '508 patent) and U.S. Pat. No. 4,956,178 (hereinafter the '178 patent), and submucosal tissue graft compositions derived from urinary bladder have been described in U.S. Pat. No. 5,554,389 (hereinafter the '389 patent). All of these compositions consist essentially of the same tissue layers and are prepared by the same method, the difference being that the starting material is small intestine on the one hand and urinary bladder on the other. The procedure detailed in the '508 patent, incorporated by reference in the '389 patent and the procedure detailed in the '178 patent, includes mechanical abrading steps to remove the inner layers of the tissue, including at least the luminal portion of the tunica mucosa of the intestine or bladder, i.e., the lamina epithelialis mucosa (epithelium) and lamina propria, as detailed in the '178 patent. Abrasion, peeling, or scraping the mucosa delaminates the epithelial cells and their associated basement membrane, and most of the lamina propria, at least to the level of a layer of organized dense connective tissue, the stratum compactum. Thus, the tissue graft material previously recognized as soft tissue replacement material is devoid of epithelial basement membrane and consists of the submucosa and stratum compactum.
The epithelial basement membrane is a thin sheet of extracellular material contiguous with the basilar aspect of epithelial cells. Sheets of aggregated epithelial cells of similar type form an epithelium. Epithelial cells and their associated epithelial basement membrane are positioned on the luminal portion of the tunica mucosa and constitute the internal surface of tubular and hollow organs and tissues of the body. Epithelial cells and their associated epithelial basement membrane are also positioned on the external surface of the body, i.e., skin. Examples of a typical epithelium having a basement membrane include, but are not limited to the following: the epithelium of the skin, intestine, urinary bladder, esophagus, stomach, cornea, and liver. Epithelial cells are positioned on the luminal or superficial side of the epithelial basement membrane, opposite to connective tissues. Connective tissues, the submucosa, for example, are positioned on the abluminal or deep side of the basement membrane. Examples of connective tissues that are positioned on the abluminal side of the epithelial basement membrane are the submucosa of the intestine and urinary bladder, and the dermis and subcutaneous tissues of the skin.